Multichannel heat exchanger fins

ABSTRACT

Heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) systems and heat exchangers are provided that include nubbed, collared, and/or flapped fins. In certain embodiments, the fins include openings or slots with protrusions for spacing multichannel tubes from the fins. During assembly, the protrusions may be deformed by the tubes. Braze alloy may be positioned in the gaps created by the protrusions to affix the multichannel tubes to the fins. In other embodiments, the fins include flaps or collars designed to interface with the multichannel tubes. In these embodiments, the tubes may be expanded into the fins.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 61/232,119, entitled “MULTICHANNEL HEAT EXCHANGER FINS”, filed Aug. 7, 2009, which is hereby incorporated by reference.

BACKGROUND

The invention relates generally to multichannel heat exchanger fins.

Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger. Each multichannel tube may contain several individual flow channels. As a fluid, such as refrigerant, flows through the flow channels, the fluid may exchange heat with an external fluid, such as air, flowing between the multichannel tubes. Multichannel heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems.

Fins are positioned between the multichannel tubes to facilitate heat transfer between the refrigerant contained within the tubes and the external air passing over the tubes. Typically, multichannel heat exchangers include corrugated sets of fins that are placed in between and parallel to adjacent tubes. The crests of the fins may be brazed or otherwise joined to the adjacent tubes. However, due to the relatively small interstices between the crests, water may tend to collect on the fins, thereby reducing thermal transfer capabilities by closing flow paths for air. This may be particularly problematic for heat exchangers, such as heat pumps, functioning as evaporators in an outdoor location.

Plate fins, extending generally transverse to tubes, may be used instead of corrugated fins to inhibit condensate collection. Plate fin heat exchangers are typically assembled by inserting the tubes through openings in the fins and then outwardly expanding the tubes. A bullet, or similar object, may be inserted within the tubes to expand the tubes into the fins. However, the multiple individual flow channels within the multichannel tubes may make this type of assembly problematic.

SUMMARY

The present invention relates to a heat exchanger that includes a first manifold, a second manifold, and a plurality of multichannel tubes in fluid communication with the first and second manifolds, each multichannel tube having a plurality of generally parallel flow paths extending through a cross section of the multichannel tube. The heat exchanger also includes a plurality of fins coupled to the plurality of multichannel tubes, the fins having openings disposed around the cross sections, and a plurality of projections protruding into the openings to contact the multichannel tubes within openings.

The present invention also relates to a heat exchanger fin that includes a sheet of thermally conductive material, elongated openings formed in the sheet for receiving multichannel tubes, and a plurality of projections extending into each of the openings for contacting the multichannel tubes upon insertion through the openings.

The present invention further relates to a method for making a heat exchanger that includes inserting a multichannel tube coated with a braze alloy through a plurality of openings each disposed on a sheet of thermally conductive material with a plurality of projections extending into the opening to contact the multichannel tube, and conveying the multichannel tube and the sheets of thermally conductive material through an oven to permanently join the multichannel tube to the sheets of thermally conductive material by retaining the braze alloy between the plurality of projections.

DRAWINGS

FIG. 1 is an illustration of an exemplary embodiment of a commercial or industrial HVAC&R system that employs heat exchangers with nubbed fins.

FIG. 2 is an illustration of an exemplary embodiment of a residential HVAC&R system that employs heat exchangers with nubbed fins.

FIG. 3 is an exploded view of the outdoor unit shown in FIG. 2.

FIG. 4 is a diagrammatical overview of an exemplary air conditioning system that may employ one or more heat exchangers with nubbed fins.

FIG. 5 is a diagrammatical over of an exemplary heat pump system that may employ one or more heat exchangers with nubbed fins.

FIG. 6 is a perspective view of an exemplary embodiment of a heat exchanger containing multichannel tubes and nubbed fins.

FIG. 7 is a partially exploded view of a portion of the heat exchanger of FIG. 6.

FIG. 8 is a front view of one of the fins shown in FIG. 6.

FIG. 9 is a detail view of one of the openings shown in FIG. 8.

FIG. 10 is a detail view of the opening of FIG. 9 with a tube inserted in the opening.

FIG. 11 is a front view of another exemplary fin with nubs.

FIG. 12 is a perspective view of a portion of a multi-slab heat exchanger employing nubbed fins and curved tubes.

FIG. 13 is a front view of another exemplary fin with slots and nubs.

FIG. 14 is a front view of the fin of FIG. 13 with tubes inserted through the openings.

FIG. 15 is a front view of another exemplary fin with angled slots and nubs.

FIG. 16 is a front view of another exemplary fin with larger slots.

FIG. 17 is a partially exploded view of a portion of a heat exchanger employing collared fins.

FIG. 18 a partially exploded view of a portion of a heat exchanger employing fins with flapped openings.

FIG. 19 is a front view of one of the fins shown in FIG. 18.

FIG. 20 is a front view of another embodiment of a fin with flapped openings.

FIG. 21 is a flowchart of an embodiment of a method for making a heat exchanger.

FIG. 22 is a flowchart of another embodiment of a method for making a heat exchanger.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict exemplary applications for heat exchangers employing plate fins with nubs or tabs for retaining multichannel heat exchanger tubes. The plate fins may generally include openings with projections, such as nubs or flaps, protruding into the openings. During assembly, the projections may deform as they are contacted by the tubes. In certain embodiments, the projections may interface with the tubes to space the tubes from the fins to form openings for receiving a braze alloy, which during heating may affix the tubes to the fins. Further, the projections may produce an interference fit between the fins and the tubes.

Such systems, in general, may be applied in a range of settings, both within the HVAC&R field and outside of that field. In presently contemplated applications, however, heat exchangers may be used in residential, commercial, light industrial, industrial, and in any other application for heating or cooling a volume or enclosure, such as a residence, building, structure, and so forth. Moreover, the heat exchangers may be used in industrial applications, where appropriate, for basic refrigeration and heating of various fluids. The configurations may be particularly well-suited to heat exchangers functioning as outdoor evaporation units, such as those used in heat pumps.

FIG. 1 illustrates an exemplary application, in this case an HVAC&R system for building environmental management that may employ heat exchangers. A building 10 is cooled by a system that includes a chiller 12 and a boiler 14. As shown, chiller 12 is disposed on the roof of building 10 and boiler 14 is located in the basement; however, the chiller and boiler may be located in other equipment rooms or areas next to the building. Chiller 12 is an air cooled or water cooled device that implements a refrigeration cycle to cool water. Chiller 12 may be a stand-alone unit or may be part of a single package unit containing other equipment, such as a blower and/or integrated air handler. Boiler 14 is a closed vessel that includes a furnace to heat water. The water from chiller 12 and boiler 14 is circulated through building 10 by water conduits 16. Water conduits 16 are routed to air handlers 18, located on individual floors and within sections of building 10.

Air handlers 18 are coupled to ductwork 20 that is adapted to distribute air between the air handlers. In certain embodiments, the ductwork may receive air from an outside intake (not shown). Air handlers 18 include heat exchangers that circulate cold water from chiller 12 and hot water from boiler 14 to provide heated or cooled air. Fans, within air handlers 18, draw air through the heat exchangers and direct the conditioned air to environments within building 10, such as rooms, apartments, or offices, to maintain the environments at a designated temperature. A control device, shown here as including a thermostat 22, may be used to designate the temperature of the conditioned air. Control device 22 also may be used to control the flow of air through and from air handlers 18. Other devices may, of course, be included in the system, such as control valves that regulate the flow of water and pressure and/or temperature transducers or switches that sense the temperatures and pressures of the water, the air, and so forth. Moreover, control devices may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building.

FIG. 2 illustrates a residential heating and cooling system. In general, a residence 24 will include refrigerant conduits 26 that operatively couple an indoor unit 28 to an outdoor unit 30. Indoor unit 28 may be positioned in a utility room, an attic, a basement, and so forth. Outdoor unit 30 is typically situated adjacent to a side of residence 24 and is covered by a shroud to protect the system components and to prevent leaves and other contaminants from entering the unit. Refrigerant conduits 26 transfer refrigerant between indoor unit 28 and outdoor unit 30, typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction.

When the system shown in FIG. 2 is operating as an air conditioner, a heat exchanger in outdoor unit 30 serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit 28 to outdoor unit 30 via one of the refrigerant conduits 26. In these applications, a heat exchanger of the indoor unit, designated by the reference numeral 32, serves as an evaporator. Evaporator 32 receives liquid refrigerant (which may be expanded by an expansion device, not shown) and evaporates the refrigerant before returning it to outdoor unit 30.

Outdoor unit 30 draws in environmental air through its sides as indicated by the arrows directed to the sides of the unit, forces the air through the outer unit heat exchanger by a means of a fan (not shown), and expels the air as indicated by the arrows above the outdoor unit. When operating as an air conditioner, the air is heated by the condenser heat exchanger within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. Air is blown over indoor heat exchanger 32 and is then circulated through residence 24 by means of ductwork 20, as indicated by the arrows entering and exiting ductwork 20. The overall system operates to maintain a desired temperature as set by thermostat 22. When the temperature sensed inside the residence is higher than the set point on the thermostat (plus a small amount), the air conditioner will become operative to refrigerate additional air for circulation through the residence. When the temperature reaches the set point (minus a small amount), the unit will stop the refrigeration cycle temporarily.

When the unit in FIG. 2 operates as a heat pump, the roles of the heat exchangers are reversed. That is, the heat exchanger of outdoor unit 30 will serve as an evaporator to evaporate refrigerant and thereby cool air entering outdoor unit 30 as the air passes over the outdoor unit heat exchanger. Indoor heat exchanger 32 will receive a stream of air blown over it and will heat the air by condensing a refrigerant.

FIG. 3 illustrates a partially exploded view of one of the units shown in FIG. 2, in this case outdoor unit 30. Unit 30 includes a shroud 34 that surrounds the sides of unit 30 to protect the system components. Adjacent to shroud 34 is a heat exchanger 36. A cover 38 encloses a top portion of heat exchanger 36. Foam 40 is disposed between cover 38 and heat exchanger 36. A fan 42 is located within an opening of cover 38 and is powered by a motor 44. A wire way 46 may be used to connect motor 44 to a power source. A fan guard 48 fits within cover 38 and is disposed above the fan to prevent objects from entering the fan.

Heat exchanger 36 is mounted on a base pan 50. Base pan 50 provides a mounting surface and structure for the internal components of unit 30. A compressor 52 is disposed within the center of unit 30 and is connected to another unit within the HVAC&R system, for example an indoor unit, by connections 54 and 56 that connect to conduits circulating refrigerant within the HVAC&R system. A control box 58 houses the control circuitry for outdoor unit 30 and is protected by a cover 60. A panel 62 may be used to mount control box 58 to unit 30.

Refrigerant enters unit 30 through vapor connection 54 and flows through a conduit 64 into compressor 52. The vapor may be received from the indoor unit (not shown). After undergoing compression in compressor 52, the refrigerant exits compressor 52 through a conduit 66 and enters heat exchanger 36 through inlet 68. Inlet 68 directs the refrigerant into a manifold or header 70. From header 70, the refrigerant flows through heat exchanger 36 to a manifold or header 72. From header 72 the refrigerant flows back through heat exchanger 36 and exits through an outlet 74 disposed on header 70. After exiting heat exchanger 36, the refrigerant flows through conduit 76 to liquid connection 56 to return to the indoor unit where the process may begin again.

FIG. 4 illustrates an air conditioning system 78, which may employ multichannel tube heat exchangers with nubbed plate fins. Refrigerant flows through system 78 within closed refrigeration loop 80. The refrigerant may be any fluid that absorbs and extracts heat. For example, the refrigerant may be hydrofluorocarbon (HFC) based R-410A, R-407, or R-134a, or it may be carbon dioxide (R-744A) or ammonia (R-717). Air conditioning system 78 includes control devices 82 that enable the system to cool an environment to a prescribed temperature.

System 78 cools an environment by cycling refrigerant within closed refrigeration loop 80 through a condenser 84, a compressor 86, an expansion device 88, and an evaporator 90. The refrigerant enters condenser 84 as a high pressure and temperature vapor and flows through the multichannel tubes of the condenser. A fan 92, which is driven by a motor 94, draws air across the multichannel tubes. The fan may push or pull air across the tubes. As the air flows across the tubes, heat transfers from the refrigerant vapor to the air, producing heated air 96 and causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device 88 where the refrigerant expands to become a low pressure and temperature liquid. Typically, expansion device 88 will be a thermal expansion valve (TXV); however, according to other exemplary embodiments, the expansion device may be an orifice or a capillary tube. After the refrigerant exits the expansion device, some vapor refrigerant may be present in addition to the liquid refrigerant.

From expansion device 88, the refrigerant enters evaporator 90 and flows through the evaporator multichannel tubes. A fan 98, which is driven by a motor 100, draws air across the multichannel tubes. As the air flows across the tubes, heat transfers from the air to the refrigerant liquid, producing cooled air 102 and causing the refrigerant liquid to boil into a vapor. According to certain embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes.

The refrigerant then flows to compressor 86 as a low pressure and temperature vapor. Compressor 86 reduces the volume available for the refrigerant vapor, consequently, increasing the pressure and temperature of the vapor refrigerant. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor. Compressor 86 is driven by a motor 104 that receives power from a variable speed drive (VSD) or a direct AC or DC power source. According to an exemplary embodiment, motor 104 receives fixed line voltage and frequency from an AC power source although in certain applications the motor may be driven by a variable voltage or frequency drive. The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. The refrigerant exits compressor 86 as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again.

The control devices 82, which include control circuitry 106, an input device 108, and a temperature sensor 110, govern the operation of the refrigeration cycle. Control circuitry 106 is coupled to the motors 94, 100, and 104 that drive condenser fan 92, evaporator fan 98, and compressor 86, respectively. Control circuitry 106 uses information received from input device 108 and sensor 110 to determine when to operate the motors 94, 100, and 104 that drive the air conditioning system. In certain applications, the input device may be a conventional thermostat. However, the input device is not limited to thermostats, and more generally, any source of a fixed or changing set point may be employed. These may include local or remote command devices, computer systems and processors, and mechanical, electrical and electromechanical devices that manually or automatically set a temperature-related signal that the system receives. For example, in a residential air conditioning system, the input device may be a programmable 24-volt thermostat that provides a temperature set point to the control circuitry.

Sensor 110 determines the ambient air temperature and provides the temperature to control circuitry 106. Control circuitry 106 then compares the temperature received from the sensor to the temperature set point received from the input device. If the temperature is higher than the set point, control circuitry 106 may turn on motors 94, 100, and 104 to run air conditioning system 78. The control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Other devices may, of course, be included in the system, such as additional pressure and/or temperature transducers or switches that sense temperatures and pressures of the refrigerant, the heat exchangers, the inlet and outlet air, and so forth.

FIG. 5 illustrates a heat pump system 112 that may employ multichannel tube heat exchangers with nubbed plate fins. Because the heat pump may be used for both heating and cooling, refrigerant flows through a reversible refrigeration/heating loop 114. The refrigerant may be any fluid that absorbs and extracts heat. The heating and cooling operations are regulated by control devices 116.

Heat pump system 112 includes an outside heat exchanger 118 and an inside heat exchanger 120 that both operate as heat exchangers. Each heat exchanger may function as an evaporator or a condenser depending on the heat pump operation mode. For example, when heat pump system 112 is operating in cooling (or “AC”) mode, outside heat exchanger 118 functions as a condenser, releasing heat to the outside air, while inside heat exchanger 120 functions as an evaporator, absorbing heat from the inside air. When heat pump system 112 is operating in heating mode, outside heat exchanger 118 functions as an evaporator, absorbing heat from the outside air, while inside heat exchanger 120 functions as a condenser, releasing heat to the inside air. A reversing valve 122 is positioned on reversible loop 114 between the heat exchangers to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode.

Heat pump system 112 also includes two metering devices 124 and 126 for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. The metering devices also regulate the refrigerant flow entering the evaporator so that the amount of refrigerant entering the evaporator equals, or approximately equals, the amount of refrigerant exiting the evaporator. The metering device used depends on the heat pump operation mode. For example, when heat pump system 112 is operating in cooling mode, refrigerant bypasses metering device 124 and flows through metering device 126 before entering inside heat exchanger 120, which acts as an evaporator. In another example, when heat pump system 112 is operating in heating mode, refrigerant bypasses metering device 126 and flows through metering device 124 before entering outside heat exchanger 118, which acts as an evaporator. According to other exemplary embodiments, a single metering device may be used for both heating mode and cooling mode. The metering devices typically are thermal expansion valves (TXV), but also may be orifices or capillary tubes.

The refrigerant enters the evaporator, which is outside heat exchanger 118 in heating mode and inside heat exchanger 120 in cooling mode, as a low temperature and pressure liquid. Some vapor refrigerant also may be present as a result of the expansion process that occurs in metering device 124 or 126. The refrigerant flows through multichannel tubes in the evaporator and absorbs heat from the air changing the refrigerant into a vapor. In cooling mode, the indoor air flowing across the multichannel tubes also may be dehumidified. The moisture from the air may condense on the outer surface of the multichannel tubes and consequently be removed from the air.

After exiting the evaporator, the refrigerant passes through reversing valve 122 and into a compressor 128. Compressor 128 decreases the volume of the refrigerant vapor, thereby, increasing the temperature and pressure of the vapor. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, or turbine compressor.

From compressor 128, the increased temperature and pressure vapor refrigerant flows into a condenser, the location of which is determined by the heat pump mode. In cooling mode, the refrigerant flows into outside heat exchanger 118 (acting as a condenser). A fan 130, which is powered by a motor 132, draws air across the multichannel tubes containing refrigerant vapor. According to certain exemplary embodiments, the fan may be replaced by a pump that draws fluid across the multichannel tubes. The heat from the refrigerant is transferred to the outside air causing the refrigerant to condense into a liquid. In heating mode, the refrigerant flows into inside heat exchanger 120 (acting as a condenser). A fan 134, which is powered by a motor 136, draws air across the multichannel tubes containing refrigerant vapor. The heat from the refrigerant is transferred to the inside air causing the refrigerant to condense into a liquid.

After exiting the condenser, the refrigerant flows through the metering device (124 in heating mode and 126 in cooling mode) and returns to the evaporator (outside heat exchanger 118 in heating mode and inside heat exchanger 120 in cooling mode) where the process begins again.

In both heating and cooling modes, a motor 138 drives compressor 128 and circulates refrigerant through reversible refrigeration/heating loop 114. The motor may receive power either directly from an AC or DC power source or from a variable speed drive (VSD). The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type.

The operation of motor 138 is controlled by control circuitry 140. Control circuitry 140 receives information from an input device 142 and sensors 144, 146, and 148 and uses the information to control the operation of heat pump system 112 in both cooling mode and heating mode. For example, in cooling mode, input device 142 provides a temperature set point to control circuitry 140. Sensor 148 measures the ambient indoor air temperature and provides it to control circuitry 140. Control circuitry 140 then compares the air temperature to the temperature set point and engages compressor motor 138 and fan motors 132 and 136 to run the cooling system if the air temperature is above the temperature set point. In heating mode, control circuitry 140 compares the air temperature from sensor 148 to the temperature set point from input device 142 and engages motors 132, 136, and 138 to run the heating system if the air temperature is below the temperature set point.

Control circuitry 140 also uses information received from input device 142 to switch heat pump system 112 between heating mode and cooling mode. For example, if input device 142 is set to cooling mode, control circuitry 140 will send a signal to a solenoid 150 to place reversing valve 122 in an air conditioning position 152. Consequently, the refrigerant will flow through reversible loop 114 as follows: the refrigerant exits compressor 128, is condensed in outside heat exchanger 118, is expanded by metering device 126, and is evaporated by inside heat exchanger 120. If the input device is set to heating mode, control circuitry 140 will send a signal to solenoid 150 to place reversing valve 122 in a heat pump position 154. Consequently, the refrigerant will flow through the reversible loop 114 as follows: the refrigerant exits compressor 128, is condensed in inside heat exchanger 120, is expanded by metering device 124, and is evaporated by outside heat exchanger 118.

The control circuitry may execute hardware or software control algorithms to regulate heat pump system 112. According to exemplary embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board.

The control circuitry also may initiate a defrost cycle when the system is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside heat exchanger 118 may condense and freeze on the heat exchanger. Sensor 144 measures the outside air temperature, and sensor 146 measures the temperature of outside heat exchanger 118. These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either sensor 144 or 146 provides a temperature below freezing to the control circuitry, system 112 may be placed in defrost mode. In defrost mode, solenoid 150 is actuated to place reversing valve 122 in air conditioning position 152, and motor 132 is shut off to discontinue airflow over the multichannel tubes. System 112 then operates in cooling mode until the increased temperature and pressure refrigerant flowing through outside heat exchanger 80 defrosts the heat exchanger. Once sensor 146 detects that heat exchanger 118 is defrosted, control circuitry 140 returns the reversing valve 122 to heat pump position 154. As will be appreciated by those skilled in the art, the defrost cycle can be set to occur at many different time and temperature combinations.

FIG. 6 is a perspective view of an exemplary heat exchanger that may be used in air conditioning system 78, shown in FIG. 4, or heat pump system 112, shown in FIG. 5. The exemplary heat exchanger may be a condenser 84, an evaporator 90, an outside heat exchanger 118, or an inside heat exchanger 120, as shown in FIGS. 4 and 5. It should be noted that in similar or other systems, the heat exchanger might be used as part of a chiller or in any other heat exchanging application. The heat exchanger includes manifolds 70 and 72 that are connected by multichannel tubes 164. Although 30 tubes are shown in FIG. 6, the number of tubes may vary. The manifolds and tubes may be constructed of aluminum or any other material that promotes good heat transfer. Refrigerant flows from manifold 70 through a set of first tubes 166 to manifold 72. The refrigerant then returns to manifold 70 in an opposite direction through a set of second tubes 168. The first tubes may be of identical construction to the second tubes, or the first tubes may vary from the second tubes by properties such as construction material, shape, internal flow paths, size, and the like. According to certain exemplary embodiments, the heat exchanger may be rotated approximately 90 degrees so that the multichannel tubes run vertically between a top manifold and a bottom manifold. Furthermore, the heat exchanger may be inclined at an angle relative to the vertical. Although the multichannel tubes are depicted as having an elongated and oblong shape, the tubes may be any shape, such as tubes with a cross-section in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, or parallelogram. According to exemplary embodiments, the tubes may have a diameter ranging from 0.5 mm to 3 mm with a wall thickness and an inner web thickness of approximately 0.25 mm. It should also be noted that the heat exchanger may be provided in a single plane or slab, or may include bends, corners, contours, and so forth. Moreover, although a two-pass heat exchanger is depicted, the nubbed fins may be employed in single or multi-pass heat exchangers.

Refrigerant enters heat exchanger 36 through inlet 68 and exits heat exchanger 36 through outlet 74. Although FIG. 6 depicts the inlet at the top of the manifold and the outlet at the bottom of the manifold, the inlet and outlet positions may be interchanged so that the fluid enters at the bottom and exits at the top. The fluid also may enter and exit the manifold from multiple inlets and outlets positioned on bottom, side, or top surfaces of the manifold. Baffles 170 separate the inlet and outlet portions of manifold 70. Although a double baffle 170 is illustrated, any number of one or more baffles may be employed to create separation of the inlet and outlet portions. It should also be noted that according to other exemplary embodiments, the inlet and outlet might be contained on separate manifolds, eliminating the need for a baffle.

Fins 172 are located around multichannel tubes 164 to promote the transfer of heat between the tubes and the environment. According to an exemplary embodiment, the fins are plate fins constructed of aluminum, interference fit or otherwise joined to the tubes, and disposed generally perpendicular to the flow of refrigerant. However, according to other exemplary embodiments, the fins may be made of other materials that facilitate heat transfer and may extend at varying angles with respect to the flow of the refrigerant. The fins may include surface features and formations such as louvers, raised lances, corrugations, ribs, and combinations thereof. Further, in certain embodiments, the fins may include spacers and/or collars for spacing the fins.

When an external fluid, such as air, flows across multichannel tubes 164, as generally indicated by airflow 174, heat transfer occurs between the refrigerant flowing within tubes 164 and the external fluid. Although the external fluid is shown here as air, other fluids may be used. As the external fluid flows across the tubes, heat is transferred to and from the tubes to the external fluid. For example, in a condenser, the external fluid is generally cooler than the fluid flowing within the multichannel tubes. As the external fluid contacts a multichannel tube, heat is transferred from the refrigerant within the multichannel tube to the external fluid. Consequently, the external fluid is heated as it passes over the multichannel tubes and the refrigerant flowing within the multichannel tubes is cooled. In an evaporator, the external fluid generally has a temperature higher than the refrigerant flowing within the multichannel tubes. Consequently, as the external fluid contacts the leading edge of the multichannel tubes, heat is transferred from the external fluid to the refrigerant flowing in the tubes to heat the refrigerant. The external fluid leaving the multichannel tubes is then cooled because the heat has been transferred to the refrigerant. In certain embodiments, a portion of the external fluid may condense and collect on the tubes and/or fins.

FIG. 7 illustrates certain components of the heat exchanger of FIG. 6 in a somewhat more detailed and exploded view. Each manifold (manifold 70 being shown in FIG. 7) is a tubular structure with open ends that are closed by a cap 178. Openings, or apertures, 180 are formed in the manifolds, such as by conventional piercing or machining operations. Multichannel tubes 164 may then be inserted into openings 180 in a generally parallel fashion. Ends 182 of the tubes are inserted into openings 180 so that fluid may flow from the manifold into flow paths 176 within the tubes.

Prior to or after insertion into manifold 70, tubes 164 may be inserted through openings 184 within fins 172 to promote heat transfer between an external fluid, such as air or water, and the refrigerant flowing within the tubes. Openings 184 encircle cross sections of tubes 164 and are disposed generally transverse to the longitudinal axis of the tubes. Fins 172 may be constructed of aluminum, aluminum alloy, copper, or the like. In certain embodiments, fins 172 may include metal sheets with openings 184 formed by stamping, punching, or other suitable manufacturing method. Openings 184 include projections, such as tabs or nubs 186 that protrude into the openings to contact tubes 166. As tubes 166 are inserted through openings 184, the nubs 186 may be bent, angled, or otherwise deformed, to hold the tubes and fins in place. In certain embodiments, some of the nubs 186 may separate from fins 172. Moreover, a lubrication material, such as thermal grease, may be applied to the tubes and/or the fins to ease assembly. The lubrication material may be compatible with the brazing material.

The heat exchanger may be brazed, or otherwise joined to hold the components together. According to certain embodiments, the tubes 166 may be coated with a braze alloy that may be applied to tubes 166 prior to or after insertion of tubes 166 within openings 184. However, in other embodiments, braze alloy, cladding material, and/or flux may be applied to the heat exchanger after tubes 166 are inserted within openings 184. After tubes 166 are inserted within openings 184, the nubs 186 contact the tubes 166 to create relatively small gaps or spaces between tubes 166 and fins 172 in the area between adjacent nubs 186. Braze alloy may fill the small gaps to join the tubes and fins to one another. In certain embodiments where the tubes are coated with a braze alloy, the braze alloy from the tubes may be drawn into the small gaps by capillary action when the heat exchanger is heated during the brazing process. Further, some or all of the nubs may be brazed to the tubes to affix the tubes to the fins.

FIG. 8 is a front view of a portion of one of the fins 172 shown in FIG. 7. Tubes 166 (FIG. 7) may be inserted through openings 184 to assemble the fins and tubes within the heat exchanger. Each opening includes a set of tabs or nubs 186 that protrude into each opening 184. As tubes are inserted through openings 184, the nubs 186 may be bent or deformed to retain the tubes 166 within the fins 172 during assembly. Surface features, such as louvers 188, may be present on fins 172 between openings 184. Furthermore, additional surface formations, such as raised lances, corrugations, ribs, spacers, and the like may be included on the fins 172. During assembly, each set of fins 172 may be stacked and aligned to receive tubes 166 through openings 184.

FIG. 9 is a detailed view of one of the openings 184 shown in FIG. 8. As shown, opening 184 includes four nubs 184, with each pair of nubs disposed opposite to each other. However, in other embodiments, the relative sizes, shapes, and positions of the nubs may vary. For example, the nubs may have a triangular shape, a pointed shape, an angular shape, a rectangular shape, or a curved shape. Further, any number of nubs in a variety of shapes and sizes may be included. For example, in other embodiments the nubs may be staggered or alternated throughout opening 184. In another example, nubs may be located on the sides or corners of opening 184. Further, in certain embodiments, different size and/or shapes nubs may be included within the same opening. Opening 184 may have a generally elliptical shape (similar to the shape of the tubes) of a width A and a height B. However, in other embodiments, the shape of the opening may vary to accommodate tubes of various cross-sectional shapes, such as circles, rectangles, and the like. The nubs 186 may extend into opening 184 to reduce the internal dimension to an internal height C that is smaller than the overall height B. The nubs 186 may extend into a portion of the opening or the nubs 186 may extend through the entire opening 184. In certain embodiments, the nubs 186 may be integrally formed with the fins 172. However, in other embodiments, the nubs may be welded, or otherwise attached to the openings.

FIG. 10 depicts the opening 184 shown in FIG. 9 with a tube 164 inserted through the opening. Tube 164 has a height D that is smaller than overall height B of opening 184. Tube 184 also has a width E, which is smaller than width A of opening 184. The smaller tube dimensions create gaps 192 between tube 164 and the fins 172. According to exemplary embodiments, the gaps may extend between tube 164 and fins 172 by a distance of approximately 0.0001 inches to 0.01 inches, and all subranges therebetween. However, in other embodiments the distance between the fins and the tubes may be smaller or larger. Although smaller than overall height B, tube height D is larger than the internal height C that is created by nubs 186. Accordingly, some or all of the nubs 186 may bend or deform as tubes 164 are inserted within the openings. Nubs 186 may generally hold tubes 164 in place during assembly. Nubs 186 also may interrupt the openings 192 to facilitate the placement of cladding material within openings 192. According to exemplary embodiments, after tubes 164 have been inserted through openings 184, a clad or coating material that causes the surface to melt at a lower temperature than the base material may be applied to fins 172, tubes 164, or both. The cladding material may wick, flow, or settle into openings 192, and when heated, may join tubes 164 to fins 172. In certain embodiments, only a portion of the openings 192 may receive the cladding material. Further, some, all, or none of the nubs 186 may be brazed to the tubes 184.

FIG. 11 depicts an embodiment of nubbed fins 194 with angled openings 196. The openings 196 are inclined with respect to the vertical at an angle F. Angle F may range from zero to 180-degrees, and all subranges therebetween. In certain embodiments, the angled openings 196 may incline the tubes at an angle with respect to the vertical to promote drainage of condensate from the tubes. Openings 196 include nubs 198 that protrude into openings 196. As described above with respect to FIGS. 8 through 10, the nubs 198 may retain the tubes within the fins during assembly, and may create gaps for the braze alloy. As shown, nubs 198 have a triangular and pointed shape, however, the size shape, and number of nubs for each opening may vary.

FIG. 12 depicts another nubbed fin 200 that may be used for multislab heat exchangers. Fins 200 are brazed, or otherwise joined, to two columns of curved tubes 202. Tubes 202 are inserted through openings 204 of a curved cross-section, slightly larger in diameter than the tubes. Nubs 206 extend into openings 204 to retain the tubes and facilitate brazing. In other embodiments, the nubbed fins may be employed for heat exchangers with any number of slabs. Further, the nubbed fins may include openings of various cross-sections, such as ellipses, circles, and the like, for receiving tubes of corresponding cross-sectional shapes.

FIGS. 13 through 16 illustrate nubbed fins with slotted openings. In certain embodiments, the slots may facilitate insertion of the tubes into the fins during assembly of the heat exchanger. Further, in certain embodiments, air may be directed over from the closed end of the slots towards the open ends of the slots to facilitate drainage of condensate.

FIG. 13 illustrates a nubbed fin 208 with slotted openings 210. The slots 210 extend completely through one side 211 of fins 208. According to exemplary embodiments, the tubes may be inserted into slots 210 through side 211 of fins 208. Nubs 212 protrude into slots 210 to retain the tubes after insertion and facilitate brazing. Slots 210 have a height G and a width H with a cross-section similar to the cross-section of the tubes.

FIG. 14 depict fins 208 with tubes 164 inserted within slots 210. The slot height G is generally larger than the tube height D so that gaps 214 are formed between the fins 208 and tubes 164. Nubs 212 extend into slots 210 to create gaps 214 between tubes 164 and fins 208 and to retain tubes 164 within fins 208 during assembly. As described above with respect to FIG. 9, braze alloy may flow or settle within some or all of the gaps 214 to join the tubes 164 to fins 208 during brazing. Length H of slot 210 may be shorter than width E of tubes 164 so that the tubes protrude slightly beyond side 211 of the fins 208.

FIG. 15 depicts another embodiment of a nubbed fin 216 with angled slots 218. Slots 218 are disposed at an angle J with respect to the vertical. Angle J may range from 0 to 180-degrees, and all subranges therebetween. According to exemplary embodiments, angled slots 218 may retain tubes 164 at angle J, which may promote the drainage of condensate 220 that may form during operation of the heat exchanger. For example, during operation, condensate 220 may flow off the edges of tubes 164 and/or the edges of fins 216. Nubs 212 protrude into slots 218 to retain tubes 164 during assembly and create gaps 212 for receiving braze alloy. As described above with respect to FIG. 9, the nubs may be deformed upon insertion of the tubes.

FIG. 16 depicts another nubbed fin 222 with slightly longer slots 224. Slots 224 may have a length K that is slightly longer than width E of tubes 164. The increased slot length K may allow the tubes 164 to be retained completely within slots 224. In certain embodiments, nubs 226 may be located at the ends of slots 224 to retain tubes 164 within slots 224. However, in other embodiments, the positions, size, and shapes of the nubs may vary. As described above with respect to FIG. 14, nubs 226 extend into the slots to retain tubes 164 during assembly and create gaps 224 for the braze alloy.

As described above with respect to FIGS. 7 to 16, nubs (e.g., 186, 198, and 206, 212, and 226) may reduce the size of openings (e.g., 124, 196, 204, and 214) to provide an interference fit for tubes 164 within the openings. However, in other embodiments, larger nubs or flaps may be employed to form complete or partial collars for receiving tubes 164. In these embodiments, tubes 164 may be interference fit within the collars. Further, in certain embodiments, tubes 164 may be expanded into the fins, for example, using hydraulic pressure, instead of, or in addition to an interference fit. In certain embodiments, hydraulic expansion may be employed to expand the tubes into the fins. Moreover, in some embodiments, the fins may be brazed to tubes 164.

FIG. 17 depicts fins 228 with collars 230 that encircle openings 231 for receiving tubes 166. Openings 231 and collars 230 may be formed by stamping, punching, roll forming, or other suitable manufacturing methods. Tubes 166 may be inserted through openings 231 in the manner described above with respect to FIG. 7. Moreover, a lubrication material, such as thermal grease, may be applied to the tubes and/or the fins to ease assembly and/or to reduce thermal resistance between the fins and the tubes, particularly when brazing may not be employed at the tube and fin interfaces. Further, in certain embodiments, the lubrication material may be compatible with the brazing material. As tubes 166 are inserted through openings 231, collars 230 may provide an interference fit that secures and/or supports tubes 166 within fins 228. Further, in certain embodiments, collars 230 may space adjacent fins 228 from one another.

In general, the internal diameter of collars 230 may be slightly smaller than the outer diameter of tubes 166 to provide an interference fit. However, in other embodiments, collars 230 may have a diameter that is greater than or equal to the outer diameter of tubes 166. In these embodiments, collars 230 may provide support for tubes 166, which may be brazed, or otherwise joined, to collars 230 and/or fins 228. For example, in certain embodiments, instead or, or in addition to brazing, hydraulic pressure may be employed to expand tubes 166 into collars 230. After tubes 166 are inserted within openings 231, the heat exchanger may be brazed, or otherwise joined to secure manifolds 70 to tubes 166. In certain embodiments, rather than brazing the entire heat exchanger, a localized torch type brazing process may be employed to heat the manifold to tube intersections of the heat exchanger. However, in other embodiments, a braze material may be applied to the heat exchanger. For example, the components (e.g., tubes, fins, and manifolds) may be clad with an alloy that melts at a lower temperature than the base material. In another example, silicon particles may be adhered to the components, which upon heating, may melt and alloy with a portion of the base material. The heat exchanger may then be conveyed through a braze furnace to create connections between the tubes and manifolds and/or between the tubes and the fins.

FIG. 18 depicts another embodiment of fins 232 with projections, such as extended nubs or flaps 234 that form partial collars. Flaps 234 may extend generally transverse to the fins 232 and may run parallel to the longitudinal axis of the tubes 166. In certain embodiments, flaps 234 may be formed when openings 231 are formed within fins 232. For example, some or all of the fin material removed to make openings 231 may be employed as flaps 234. Flaps 234 may be formed by stamping, punching, roll forming, or other suitable manufacturing methods, and may be bent outward prior to or during insertion of tubes 166. After tubes 166 have been inserted through openings 231, tubes 166 may be expanded against flaps 234 and/or may be brazed to flaps 234 and/or fins 232. For example, hydraulic expansion may be employed to expand tubes 166.

FIG. 19 is a front view of one of the fins 232 shown in FIG. 18 depicting flaps 232 prior to bending. Flaps 234 extend into openings 231 and are generally parallel to the surface of fins 232. As shown, each flap 234 extends approximately halfway into an opening 231. In certain embodiments, each opening 231 may have a height L, and each flap 234 may extend into an opening 231 at a distance that is approximately one half of height L. However, in other embodiments, flaps 234 may extend at any distance into openings 231. For example, flaps 234 may extend into openings 231 at a distance that is approximately 10, 20, 30, or 40 percent of height L.

Flaps 234 may be bent outward from fin 232 prior to or during insertion of tubes 166. Upon bending, flaps 234 may extend generally orthogonal to fins 232. However, in other embodiments, flaps 236 may extend outward from fins 232 at varying angles. In certain embodiments, flaps 234 may include scoring 236 located to facilitate bending of flaps 234. Further, openings 231 may include a space 238 between flaps 234 and fin 232 that may provide clearance for bending flaps 234. However, in other embodiments, flaps 234 may have a curvature that generally follows the perimeter of openings 231 to fill in all, or a portion of, spaces 238.

FIG. 20 depicts another embodiment of a fin 240 that includes extended nubs or flaps 242. In this embodiment, flaps 242 extend into openings 231 at a height that is approximately equal to height L. Each flap 242 extends from an opposite side of opening 231 which may allow each flap 242 to have an increased height when compared to flaps 234 shown in FIG. 19. In certain embodiments, the increased height of flaps 234 may facilitate spacing of the fins 240 by the flaps 242. For example, flaps 242 of a fin 240 may rest against an adjacent fin to space the fins 240 from one another. Furthermore, in certain embodiments, flaps 242 may include geometric features, such as bent sections or protrusions, among others, that may contact the adjacent fins 240. According to certain embodiments, flaps 242 may have a height of approximately 1.3 mm, which may allow fins 240 to be spaced from one another at approximately 1.3 mm intervals to provide approximately 19.5 fins per inch.

As may be appreciated, the flaps 234 and 242 shown in FIGS. 18-20 are provided by way of example only and are not intended to be limiting. In other embodiments, the orientation and size of flaps 234 and 242 may vary. For example, the shape, size, and/or number of flaps 234 and 242 may vary. Moreover, in other embodiments, any number of flaps in an alternating or random configuration may be employed. For example, four alternating flaps 242 may be included within an opening 231 with two flaps disposed on the upper portion of opening 231 and two flaps disposed on the lower portion of opening 231. Further, in certain embodiments, the flaps 234 and 242 may extend into the curved portions of the openings 231 and may be separated from one another around the circumferences of the openings 231 by only a small gap. Moreover, the fins shown in FIGS. 18 to 20 may include surface features, such as louvers, raised lances, corrugations, ribs, spacers, and the like.

FIG. 21 depicts an embodiment of a method 244 for making a heat exchanger that employs the fins shown in FIGS. 17 to 20. As may be appreciated, the method also may be employed to produce a heat exchanger that includes the fins shown in FIGS. 7 to 16. The method 244 may begin by forming (block 246) openings in the fins. For example, openings 231 (FIGS. 17 to 20) may be stamped, progressively stamped, roll formed, or progressively roll formed into the fins. The forming process may include forming the collars 230 shown in FIG. 17 or forming the flaps 234 and 242 shown in FIGS. 18 to 20.

Tubes may then be inserted (block 248) through the openings. In certain embodiments, the tubes may slide through the openings and bend the projections, such as the collars, nubs, and/or flaps, away from the fins. However, in other embodiments, the collars and/or the flaps may be bent prior to insertion of the tubes, for example, during the forming process. In certain embodiments, the fins may be spaced from one another, for example, using a comb, during or after insertion of the tubes through the openings. However, in other embodiments, the flaps and/or collars may space the fins from one another.

After the tubes are inserted within the fins, the headers may be brazed or otherwise joined to the tubes. For example, as shown in FIG. 17, tubes 166 may be inserted through openings 180 of header 70 and brazed to header 70. In certain embodiments, a torch brazing process may be used that applies braze material and heat to the header and tube interface.

In certain embodiments, method 244 may conclude after brazing. For example, the interference fit between the tubes and the fins may provide sufficient thermal contact between the tubes and the fins. Moreover, in certain embodiments, the fins and the tubes may be joined to one another during the brazing process. However, in other embodiments, the tubes may be expanded (block 252) to secure the tubes within the fins. For example, a hydraulic fluid, such as refrigerant oil, may be injected into header 70 to flow through tubes 166. The fluid may then be pressurized to expand the tubes. After expansion of the tubes, the hydraulic fluid may be drained or removed from the heat exchanger. In certain embodiments, the fluid may be compatible with the refrigerant designed to be used within the heat exchanger so that any fluid remaining after the hydraulic expansion process may mix with the refrigerant. In other embodiments, a gas may be used as the hydraulic fluid.

Various pressures may be employed to expand the multichannel tubes, depending on the specific design of the heat exchanger and the refrigerant intended to be used within the heat exchanger. For example, in certain embodiments, the heat exchanger may be designed for a glycol refrigerant at an operating pressure of approximately 50 psi. In these embodiments, the hydraulic fluid may be pressurized to approximately 300 psi to expand the tubes. In another example where the heat exchanger is designed to use carbon dioxide as refrigerant at an operating pressure of approximately 1400 psi, the hydraulic expansion process may use pressures of approximately 2500-3000 psi to expand the tubes. However, in other embodiments, the pressures may vary. In general, the hydraulic pressure may be greater than the operating pressure of the heat exchanger but less than the burst strength of the tubes, which, in certain embodiments, may be approximately three times the operating pressure.

In certain embodiments, the tubes may be expanded prior to assembly of the headers 70 to the tubes 166. FIG. 22 depicts a method 254 where the tubes may be expanded prior to insertion within the headers. The method 254 may begin by forming (block 256) openings in the fins and inserting (block 258) the tubes through the openings. For example, the openings may be formed and the tubes may be inserted through the openings as described above with respect to FIG. 21.

The tubes may then be expanded (block 260) for example, by use of a hydraulic expansion process, as described above with respect to FIG. 21. In certain embodiments, each tube may be expanded individually upon insertion through the fins. However, in other embodiments groups of tubes may be expanded together using an expansion tool or other suitable method. After the tubes have been expanded, the heat exchanger may then be brazed (block 262). For example, the tubes may be inserted within the headers and brazed to the headers using a torch brazing method. However, in other embodiments, the entire heat exchanger assembly may be conveyed through a braze oven. Furthermore, in certain embodiments, the tubes and fins may be brazed together during the brazing process.

It should be noted that the present discussion makes use of the term “multichannel” tubes or “multichannel heat exchanger” to refer to arrangements in which heat transfer tubes include a plurality of flow paths between manifolds that distribute flow to and collect flow from the tubes. A number of other terms may be used in the art for similar arrangements. Such alternative terms might include “microchannel” and “microport.” The term “microchannel” sometimes carries the connotation of tubes having fluid passages on the order of a micrometer and less. However, in the present context such terms are not intended to have any particular higher or lower dimensional threshold. Rather, the term “multichannel” used to describe and claim embodiments herein is intended to cover all such sizes. Other terms sometimes used in the art include “parallel flow” and “brazed aluminum.” However, all such arrangements and structures are intended to be included within the scope of the term “multichannel.” In general, such “multichannel” tubes will include flow paths disposed along the width or in a plane of a generally flat, planar tube, although, again, the invention is not intended to be limited to any particular geometry.

While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation. 

1. A heat exchanger comprising: a first manifold; a second manifold; a plurality of multichannel tubes in fluid communication with the first and second manifolds, each multichannel tube having a plurality of generally parallel flow paths extending through a cross section of the multichannel tube; a plurality of fins coupled to the plurality of multichannel tubes, the fins having openings disposed around the cross sections; and a plurality of projections protruding into the openings to contact the multichannel tubes within the openings.
 2. The heat exchanger of claim 1, comprising braze alloy disposed between the projections to affix the multichannel tubes to the fins.
 3. The heat exchanger of claim 1, wherein the plurality of multichannel tubes are coated with a braze alloy, and wherein the plurality of projections are configured to draw the braze alloy from the tubes by capillary action.
 4. The heat exchanger of claim 1, wherein the projections are configured to deform upon contacting one of the multichannel tubes.
 5. The heat exchanger of claim 1, wherein the openings encircle the cross sections of the multichannel tubes.
 6. The heat exchanger of claim 1, wherein the projections comprise nubs that define an internal height of the openings that is smaller than a cross sectional height of the multichannel tubes.
 7. The heat exchanger of claim 1, wherein the projections comprise flaps that extend into the openings from opposite sides of the openings to produce an interference fit between the multichannel tubes and the fins.
 8. The heat exchanger of claim 1, wherein the plurality of multichannel tubes are expanded into the fins.
 9. A heat exchanger fin comprising: a sheet of thermally conductive material; elongated openings formed in the sheet for receiving multichannel tubes; and a plurality of projections extending into each of the openings for contacting the multichannel tubes upon insertion through the openings.
 10. The heat exchanger fin of claim 9, wherein each of the openings is completely surrounded by the sheet of thermally conductive material.
 11. The heat exchanger fin of claim 9, wherein the plurality of projections are integrally formed in the sheet of thermally conductive material.
 12. The heat exchanger fin of claim 9, wherein the plurality of projections comprises a plurality of nubs extending into each of the openings for contacting the multichannel tubes upon insertion through the openings.
 13. The heat exchanger fin of claim 12, wherein the nubs are aligned in pairs, with each nub of a pair extending towards the other nub of the pair from an opposite side of the opening.
 14. The heat exchanger fin of claim 9, wherein the plurality of projections comprises flaps extending into the openings from the sheet and separated from one another around the circumferences of the openings.
 15. A method for making a heat exchanger comprising: inserting a multichannel tube coated with a braze alloy through a plurality of openings each disposed on a sheet of thermally conductive material with a plurality of projections extending into the opening to contact the multichannel tube; and conveying the multichannel tube and the sheets of thermally conductive material through an oven to permanently join the multichannel tube to the sheets of thermally conductive material by retaining the braze alloy between the plurality of projections.
 16. The method of claim 15, wherein inserting a multichannel tube comprises deforming at least one projection with the multichannel tube.
 17. The method of claim 15, wherein conveying the multichannel tube and the sheets of thermally conductive material through an oven comprises drawing the braze alloy from the multichannel tube into spaces between the plurality of projections.
 18. The method of claim 15, comprising forming the plurality of openings within the sheets of thermally conductive material, wherein forming the plurality of openings comprises forming flaps extending into the plurality of openings, wherein the flaps are designed to interface with the multichannel tube.
 19. The method of claim 15, comprising forming the plurality of openings within the sheets of thermally conductive material, wherein forming the plurality of openings comprises forming nubs extending into the plurality of openings to create spaces therebetween for receiving the braze alloy.
 20. The method of claim 15, comprising inserting an end of the multichannel tube into a header and permanently joining the multichannel tube and the header. 